In the beginning of modern wireless telecommunications, a briefcase-sized “mobile” device allowed users to make phone calls into the historic public switched telephone network (PSTN). Since this early beginning, wireless technology has advanced with mobile phones becoming smaller and more powerful, while mobile networks have advanced data download speeds and bandwidth capabilities. These mobile systems are to the point that mobile phones are now typically considered mobile or wireless devices that have merged traditional phones with portable computers. Mobile devices are capable of running complex software applications and often have multiple wireless access technologies to communicate voice and data using both short-range and long-range wireless systems. With this decrease in size and substantial increase in processing power and memory, the power demands of new mobile devices are now generally balanced against the power available from smaller batteries; which keep getting smaller to fit into the smaller, more complex devices. Therefore, battery life and power management are keys to continuing the advancement of the mobile revolution.
In considerations of future wireless networks, i.e., more advanced versions of 3G and beyond, the Third Generation Partnership Project (3GPP) considers the Universal Mobile Telecommunications System (UMTS) as a strong candidate for future high speed packet data networks in its Long Term Evolution (LTE) systems. In most mobile communication networks, including UMTS, power management at the wireless device or user equipment (UE) is extremely important to support a high rate of multimedia packet services. Thus, the preservation of battery power greatly affects both the mobility of the wireless device and the quality of service (QoS) received.
Several power saving mechanisms have been proposed for extending the battery life in mobile devices. One such method that has been implemented is the use of a sleep or idle mode in mobile devices. When in standby mode (i.e., the mode in which there are no active transmissions or active downloads occurring at the device) and there is no data scheduled for transmission over the wireless link between the mobile device and base station, the mobile device transitions into a sleep or idle mode. The idle mode physically or electronically shuts down power to as many functional units as possible within the mobile device. Idle mode, then, typically consumes the power used to maintain the essential device resources, such as volatile memory and the systems that monitor the paging and control channels of the wireless network.
One application used with this idle mode mechanism in UMTS is discontinuous reception (DRX). In DRX, the network typically assigns a unique paging indicator (PI) that will be broadcasted once per paging message schedule or paging occasion (PO) during the DRX cycle. Because the mobile device knows its unique PI and knows when the PO occurs during a particular DRX cycle length, the mobile device may enter idle mode and, when the PO time arises, the device wakes up temporarily and powers the long-range receiver to monitor the paging channel (PCH) for its PI and any paging messages. Paging messages may include messages that alert the mobile device to the occurrence of an incoming call, changes to control/overhead messages that carry system information and other information for the mobile device, and the like. If there is no paging message, the device reenters the idle mode and waits for the next scheduled PO transmission. This sequence of switching functional parts of the mobile device on and off during the idle mode is often referred to as the slotted mode of operation.
Similarly, system designers generally select to institute particular slot cycles or POs based on balancing the effects of power savings vs. phone responsiveness. Longer slot cycles or POs increase power savings as the receiver and other non-essential functional parts of the mobile device may be shut down longer. However, the longer slot cycle also means that it will take longer for the mobile device to recognize that it has incoming messages. Conversely, shorter slot cycles or POs increase the responsiveness of the mobile device to its pages, but does not conserve as much power.
Because most wireless devices are not constantly receiving or transmitting data, they spend a large majority of their time in idle mode. However, as noted, idle mode includes a constant and systematic cycle of start-ups and idle-downs of the long-range receiver to check for paging messages. The long-range receiver is a power hungry part of a mobile device. While the ability to conserve battery power during the idle times provides a power-saving benefit, the constant cycling of the device on and off still draws a non-negligible amount of power from the battery. For example, in wireless devices compliant with Code Division Multiple Access (CDMA) (including Wideband Code Division Multiple Access (W-CDMA)) and/or Global System for Mobile Communications (GSM) standards, current consumption in idle mode may be as high as a few milli-amperes (mA) as a result of the long-range receiver cycling on and off. As a result of this current consumption, the available battery power still decreases at a non-negligible rate during idle time, thus, shortening the useful mobility of the device.